Turbochargers are used in conjunction with internal combustion engines in vehicles (e.g., trucks, automobiles, tractors, etc.) to increase power output, improve efficiency, lower emissions or to achieve a combination of these advantages or improvements. A turbocharger is comprised of a turbine that converts kinetic energy in the combustion products exhausted from the engine into mechanical work that is transmitted to a compressor that draws in ambient air and discharges the air at a higher pressure. The higher pressure air discharged from the turbocharger compressor is conveyed to the air intake manifold of the internal combustion engine, providing a higher mass flow of oxygen to the cylinders. The increased mass flow of oxygen is accompanied by an increased mass flow of fuel to the cylinders leading to more combustion and power per piston stroke.
While turbocharger performance depends on a variety of factors, as a general rule, the responsiveness of a turbocharged system can be increased by decreasing the effective inducer radius for a given compressor wheel having a fixed exducer radius. However, this is typically accompanied by a reduction in the maximum power that can be achieved by the system. Reciprocally, the maximum achievable power can generally be increased by increasing the effective inducer radius for a given compressor wheel having a fixed exducer radius. Thus, for a balanced turbocharged system that provides some combination of increased power, increased fuel efficiency, and reduced harmful emissions, there is a trade-off between the maximum power than can be developed by the turbocharged system and the responsiveness of the system (i.e., the time it takes to reach maximum power).
Typically, the relationship between exducer radius and inducer radius is fixed, with the compressor housing being deliberately designed so that the air inlet to the compressor wheel has a diameter greater than the diameter of the inducer portion of the compressor wheel. However, Patent Application Publication No. US 2014/0308110 A1 discloses that the inlet cross-sectional area to the inducer portion of the compressor wheel can be altered by effectively reducing the inducer area of the compressor wheel to reduce lag time or spool-up time (i.e., the time it takes to increase the rotational speed of the compressor wheel sufficiently to achieve increased power output from the turbocharged system), and increase efficiency, but at the expense of reduced maximum power. This document also teaches that the effective inducer area can be increased to increase the maximum power output, but at the expense of reduced efficiency and responsiveness.
Patent Application Publication No. 2014/0308110 discloses various adjustable wall compressor housings and mechanical or fluid-mechanical mechanisms for adjusting the housing geometry via a controller in response to various parameters, such as engine power demand, engine emissions, atmospheric pressure, compressor back pressure, exhaust back pressure, ambient temperature, compressed air temperature, exhaust gas recirculation, etc. This complex arrangement may have some value in certain applications. However, variable geometry compressor housings responsive to operating parameters require many sensors and many moving parts that are expensive and more susceptible to failure than fixed geometry compressor housings.
While conventional fixed geometry compressor housings are highly reliable and considerably less expensive than variable geometry compressor housings, they cannot be easily reconfigured or tuned as desired to trade between power and responsiveness or between power and efficiency.